Add shouldExpect() mocking method

[LucasBrunner]

This PR adds the static shouldExpect method to the AsFake trait.

This exposes the behavior of Mockery's ->expects(). Users will now be able to use ::shouldExpect() to declare that a mocked action should run once and only once.

Fixes #278

[lorisleiva]

Thanks for this! I'm just not a great fan of the method name shouldExpect because that is not how the fluent API of expects is supposed to start with.

The current helper shouldRun makes sense because the underlying fluent API starts with shouldReceive.

I think expects would be better but would be more likely to cause a conflict with existing method names.

In any case this introduces a breaking change by adding a function to everyone's action class and I'm not sure this little change warrants a bump to v3.

@Wulfheart what do you think?

[Wulfheart]

@lorisleiva no opinion on that. However, if you say it is inconsistent that I would be against it in its current form and be open for another naming. It still seems useful on first thought.

[LucasBrunner]

I agree that the name shouldExpect is not great and changing it is no problem.

It's a great point that since AsFake is a trait adding methods to it could result in namespace collisions with the class using it. Since this means a version bump I would like to take the opportunity to suggest a few further additions to improve the testing experience, but those ideas are more substantial changes than this so I will make dedicated issues for them.